The U.S. Treasury Department as well as the Internal Revenue Service issued on Thursday new rules that are aimed at discouraging companies based in the U.S. from moving their corporate domicile abroad searching for lower rates for taxes.

American companies are increasingly trying to lower tax liabilities through this tactic call corporate inversion – acquiring a smaller competitor overseas and using the purchase to move its headquarters to countries that have tax rates that are more favorable than the U.S.

The new measures will make it more difficult by curbing the ability of the companies to avoid tax rates in the U.S. of they move to other locations where they lack significant business activity.

Yet one possible target for the action by the Treasury Department, Pfizer, is weighing its ways to bypass the rules that govern the inversions as they seek to buy Allergan a fellow drug maker, based in Ireland for close to $150 billion.

Amongst the strategies its discussing, is the structuring of the transaction so that Allergan technically is the buyer, according to a source close to the situation.

Since the headquarters of Allergan are in Ireland already, even though a great deal of its operation is located in New Jersey, the deal could allow them to avoid being called an inversion.

However, in reality, Pfizer, has a market value of $205 billion and would effectively be purchasing its counterpart that has a capitalization of close to $124 billion.

Its shares would have 55% of the new combined business and shareholders of Allergan would be given a premium for the holdings they have said the person.

A deal is likely within the next week said the source, who cautioned that the talks were continuing and might still not reach an agreement.

Pfizer and Allegan representatives would not comment when contacted.

Reaction to these new proposed rules was muted. One law school lecturer said they turned out weaker than most had expected and will not do much to affect in a meaningful way the large deal that is about to be reached.

Get Analysts' Upgrades and Downgrades Daily - Enter your email address below to receive a concise daily summary of analysts' upgrades, downgrades and new coverage with MarketBeat.com's FREE daily email newsletter.